The present invention relates to the field of semiconductor processing, and, more particularly, to a system and associated method for treating an effluent gas from a semiconductor processing chamber.
Semiconductor processing operations typically include a chemical vapor deposition (CVD) step for depositing dielectric layers on a semiconductor wafer. The CVD process is performed in a semiconductor processing chamber. A dielectric layer typically includes silicon dioxide, which may be undoped or doped. A common approach for depositing silicon dioxide is to use a tetraethyl orthosilicate (TEOS) reagent. The TEOS reagent may also be subjected to ozone during the CVD process. As a result, the effluent gas released from the semiconductor processing chamber includes unconsumed process gases, as well as by-products of such gases. In particular, the effluent gas contains processed carbon monoxide and unreacted ozone. It is undesirable to release either of these gases into the atmosphere.
As a result of the above described CVD process, silicon dioxide is also deposited on the walls of the semiconductor processing chamber. Consequently, the walls must be periodically cleaned. A reactive ion etching (RIE) cleaning process may be performed in the semiconductor processing chamber for this purpose. Typically, fluorocarbons are used in the RIE cleaning process to remove silicon dioxide from the chamber walls. The reaction between the fluorocarbons and the deposited silicon dioxide results in the formation of carbon monoxide. The effluent gas released from the semiconductor processing chamber during the RIE cleaning process thus contains carbon monoxide.
Additionally, many other semiconductor processes result in effluent gas being released from the semiconductor processing chamber and including other unconsumed process gases, as well as by-products of such gases. A variety of gas treatment approaches have been developed to treat an effluent gas being released from a semiconductor processing chamber. A common approach is to decompose, react, or combust the undesirable gases at high temperatures.
Scrubbing with water, chemical solutions, and dry chemicals have also been used to treat an effluent gas. Water scrubbing may be used to dissolve water soluble components of the effluent gas. For contaminants which are insoluble or sparingly soluble in water, chemical scrubbing can be used. Although effective, the water or chemical absorbent must be treated prior to release. With increasingly stringent controls on water pollution, such scrubbing techniques are becoming less attractive.
Yet another approach is dilution. That is, the concentrations of undesirable species are reduced by combining the waste effluent gas with large volumes of air or an inert diluent gas. While such reduction of concentration levels may literally satisfy existing effluent gas limits, they do not result in an actual reduction in the amount of undesirable species released into the atmosphere. Moreover, as pollution regulations are sure to be tightened, the use of dilution as a method for treating an effluent gas will become less acceptable.
Dry chemical adsorption and/or reaction may also be used to treat the effluent gas. For example, the use of activated carbon beds to physically adsorb gas constituents is well established. Activated carbon, while highly efficient, scavenges gas constituents by both physical and chemical adsorption. Physically adsorbed gas constituents can later desorb unless the carbon is periodically treated by carefully controlled oxidation.
An example of an effluent gas treatment system is disclosed in U.S. Pat. No. 5,955,037 to Hoist et al. and titled xe2x80x9cEffluent Gas Stream Treatment System Having Utility For Oxidation Treatment Of Semiconductor Manufacturing Effluent Gasxe2x80x9d. In particular, the effluent gas stream treatment system includes a pre-oxidation treatment unit such as a scrubber, an oxidation unit such as an electrothermal oxidizer, and a post-oxidation treatment unit such as a wet or dry scrubber.
Another effluent gas treatment system is disclosed in U.S. Pat. No. 4,735,633 to Chiu and titled xe2x80x9cMethod and System For Vapor Extraction From Gasesxe2x80x9d. Chiu discloses a plasma extraction reactor including a pair of parallel, spaced apart electrodes for removing vapor phase waste from an effluent gas. The vapor phase waste products are converted to a solid phase deposited directly on the electrodes which then may be discarded.
In view of the foregoing background, it is therefore an object of the present invention to provide a semiconductor processing system and associated method for efficiently treating an effluent gas to remove undesired gases contained therein prior to being released into the atmosphere.
This and other objects, features and advantages in accordance with the present invention are provided by a method for treating an effluent gas released from a semiconductor processing system including the steps of exhausting the effluent gas from a processing chamber, and catalytically treating the effluent gas with the at least one mixed metal oxide. The effluent gas may be produced as a result of a chemical vapor deposition (CVD) process such as TEOS-ozone and/or from a RIE process using fluorocarbons, for example.
The effluent gas may comprise at least carbon monoxide and/or ozone. Accordingly, catalytically treating the effluent gas preferably comprises catalytically converting carbon monoxide to carbon dioxide and/or ozone to oxygen. Also, the step of catalytically treating the effluent gas may include providing at least one catalyst body having t least outer surface portions comprising the at east one mixed metal oxide, and contacting the at east one catalyst body with the effluent gas.
Objects, features and advantages in accordance with the present invention are also provided by a semiconductor processing system comprising a processing chamber having an exhaust outlet for an effluent gas, and a catalytic converter connected in fluid communication with the exhaust outlet. The catalytic converter preferably comprises at least one mixed metal oxide for catalytically treating the effluent gas. The effluent gas is treated by the catalytic converter prior to being released into the atmosphere, therefore, undesired gases, such as processed carbon monoxide and unreacted ozone resulting from semiconductor processing operations are efficiently converted into carbon dioxide and oxygen.
In one embodiment of the invention, the processing chamber comprises a chemical vapor deposition (CVD) reactor. The CVD reactor preferably comprises a TEOS source introducing TEOS reagent into the CVD reactor, and thereby causing the effluent gas to include carbon monoxide. The catalytic converter preferably catalytically converts carbon monoxide to carbon dioxide. Similarly, if ozone is introduced into the effluent gas during the CVD process, then the converter catalytically converts the ozone into oxygen. Carbon dioxide and oxygen are more environmentally desirable to release into the atmosphere. The CVD process preferably deposits a dielectric layer, such as silicon dioxide, on a semiconductor wafer. The CVD process is performed using either a thermal or plasma energy source, and preferably with a high deposition rate at low pressure.
In another embodiment of the invention, the semiconductor processing chamber comprises a plasma source for introducing plasma into the chamber for cleaning the walls. The walls are cleaned to remove dielectric material, such as silicon dioxide, deposited during the CVD process. A reactive ion etching (RIE) or plasma etching process is preferably performed for removing the silicon dioxide from the chamber walls.
Typically, fluorocarbons are used in the RIE cleaning process to remove the silicon dioxide from the chamber walls. The reaction between the fluorocarbons and the deposited silicon dioxide results in the formation of carbon monoxide. The effluent gas released from the semiconductor processing chamber during the RIE cleaning process thus contains carbon monoxide. The catalytic converter preferably catalytically converts the carbon monoxide in the effluent gas to carbon dioxide.
The at least one mixed metal oxide in the catalytic converter preferably comprises at least one hetero bi-metal oxide and/or at least one hetero tri-metal oxide. In other words, the at least one metal comprises a perovskite phase metal oxide. Hetero bi- and tri-metal oxides are catalysts for oxidation of carbon monoxide generated during the CVD process using a TEOS reagent, and during the RIE or plasma etching process for removing the silicon dioxide from the chamber walls. Likewise, the hetero bi- and tri-metal oxides are catalysts for unreacted ozone generated during the CVD process Another aspect of the present invention relates to a catalytic converter for a semiconductor processing system for treating an effluent gas released during a semiconductor processing operation. The semiconductor processing operation preferably includes a CVD process for depositing silicon dioxide on a semiconductor wafer, and a RIE cleaning process for cleaning chamber walls of the semiconductor processing system as a result of the silicon dioxide being deposited thereon during the CVD process.
The catalytic converter preferably comprises a housing having an inlet for receiving the effluent, and an outlet for releasing the effluent gas. The catalytic converter preferably comprises at least one mixed metal oxide for catalytically treating the effluent gas. The catalytic converter also preferably comprises at least one catalyst body carried by the housing, wherein the at least one mixed metal oxide is preferably coated thereon. The at least one catalyst body preferably comprises at a plurality of mesh distribution plates, a plurality of beads, or a cylindrical tube.